Here's something that I'm unable able to do on this forum compared to the previous, lock your own thread. Take this thread (http://www.lemmingsforums.net/index.php?topic=1041.0) for example. This thread reflected on the 2009 forum, but now that the new forum links all the older posts together I don't see any point of editing this. This process is obviously a request that I could easily PM a moderator for.
There should be a link near the bottom of a topic (along with a link to move the topic and one to delete it.) Just above the quickpost box, if you have it enabled.
Ah yes, found it! I just couldn't see the brightly coloured un-outlined boxes. :P Thanks.